1. Field of the Invention
The invention relates to a vehicle bearing apparatus.
2. Description of Related Art
There has been conventionally known a technique as described in Japanese Patent Application Publication No. 2010-83432 (JP 2010-83432 A), as a configuration of a vehicle bearing apparatus in which a drive shaft is connected to a hub spindle of a hub wheel such that rotation of the drive shaft is transmittable to the hub spindle. JP 2010-83432 A describes a technique in which a spline is formed on a vehicle body side flat end face of the hub spindle of the hub wheel, and a spline is formed also on an outer-side flat end face of a constant velocity joint disposed at an end portion of the drive shaft. Further, JP 2010-83432 A describes the following technique. In a state where tooth flanks of the splines formed on these two flat surfaces, that is, side-face splines are engaged with each other, pressure is applied to the engagement surfaces in a direction perpendicular to the engagement surfaces by fastening the hub spindle of the hub wheel and the constant velocity joint together, with a nut, from the axial direction of the hub spindle. In this way, the hub spindle and the constant velocity joint are connected to each other.
As illustrated in FIG. 8, when tooth tips 128, 148 of side-face splines 126, 146 of the hub spindle of the hub wheel and the constant velocity joint are each formed as a flat surface that is perpendicular to the direction of the axis of rotation of the hub spindle, the tooth tips 128, 148 may make surface contact with each other in a state where the tooth tips 128, 148 are opposed to each other. When the tooth tips 128, 148 are opposed to each other, even if pressure is applied to the hub spindle of the hub wheel and the constant velocity joint in the axial direction, a normal engagement state in which tooth flanks 127, 147 of the side-face splines 126, 146 make surface contact with each other is not achieved, and therefore the hub spindle of the hub wheel and the constant velocity joint are connected in an inappropriate engagement state.
In view of this, JP 2010-83432 A describes two techniques for preventing the above-described conventional side-face splines from being engaged inappropriately. The techniques described in JP 2010-83432 A are illustrated in FIGS. 9 and 10.
As the first technique, a side-face spline 226 of a hub spindle of a hub wheel has flat tooth flanks 227 and tooth tips 228 formed as curved surfaces, as illustrated in FIG. 9. Similarly, a side-face spline 246 of a constant velocity joint has flat tooth flanks 247 and tooth tips 248 formed as curved surfaces. The hub spindle of the hub wheel and the constant velocity joint are connected to each other by engaging the side-face spline 226 and the side-face spline 246 with each other through application of pressure in the axial direction. At this time, when the side-face spline 226 make line contact with the side-face spline 246 with the curved-surface portions of the tooth tips 228 and the curved-surface portions of the tooth tips 248 opposed each other, the tooth tips 228 slip down over the tooth tips 248 and move toward bottom lands 249. Similarly, the tooth tips 248 slip down over the tooth tips 228 and move toward bottom lands 229. Thus, the side-face spline 226 and the side-face spline 246 rotate relative to each other, and flat portions of the tooth flank 227 and flat portions of the tooth flank 247 make surface contact with each other, thereby achieving a normal engagement state.
As illustrated in FIG. 10 as the second technique, each side-face spline 326 of a hub spindle of a hub wheel is configured such that a tooth tip 328 on which flat tooth flanks 327 intersect each other is formed, and the whole tooth is formed in a shape of an acute triangle. Further, each bottom land 329 is formed in a shape corresponding to a tooth tip 348 of each side-face spline 346 of a constant velocity joint. Similarly, each side-face spline 346 of the constant velocity joint is configured such that the tooth tip 348 at which flat tooth flanks 347 intersect each other is formed, and the whole tooth is formed in a shape of an acute triangle. Further, a bottom land 349 is formed in a shape corresponding to the tooth tip 328 of each side-face spline 326 of the hub spindle of the hub wheel. The hub spindle of the hub wheel and the constant velocity joint are connected to each other by engaging the side-face spline 326 and the side-face spline 346 with each other through application of pressure in the axial direction. At this time, the tooth tips 328 of the side-face spline 326 and the tooth tips 348 of the side-face spline 346 may face each other. At this time, the tooth tips 328 move to slip down over the tooth flanks 347 and engage with the bottom lands 349. Similarly, the tooth tips 348 move to slip down over the tooth flanks 327 and engage with the bottom lands 329. Thus, the side-face spline 326 and the side-face spline 346 rotate relative to each other, and flat portions of the tooth flank 327 and flat portions of the tooth flank 347 make surface contact with each other, thereby achieving a normal engagement state.
However, the techniques described in JP 2010-83432 A have the following inconveniences. Initially, engagement portions of the side-face spline 226 and the side-face spline 246 described in the first technique are the flat portions of the tooth flanks 227 and the tooth flanks 247. However, in order to join the tooth flanks 227 and the tooth tip 228 together smoothly at the boundaries, the tooth flanks 227 and the tooth tip 228 are joined together so that portions near the boundaries have a partially round shape. Therefore, the portions of the tooth flanks 227, which are near the boundaries with the tooth tip 228, are not flat and do not engage with the tooth flanks 247. Therefore, the amount of the flat portion of each tooth flank 227 is decreased, which causes a decrease in the engagement area. The same applies to the boundaries between the tooth flanks 247 and the tooth tip 248.
In the second technique of connecting the hub spindle of the hub wheel and the constant velocity joint to each other, the whole tooth of each of the side-face splines 326, 346 is formed in a shape of an acute triangle, and each of the bottom lands 329, 349 has a shape corresponding to the acute triangle. Therefore, if the tooth tips 328, 348 do not completely match the bottom lands 329, 349, backlash may occur after the hub spindle of the hub wheel is fitted to the constant velocity joint.